tl;dr - if we did then we'd have to admit that maybe we didn't deserve to be as successful as we are.
(Also - from my own ignorant past - I didn't tend to be in the room when people are being actively sexist, and didn't directly experience it. And until a couple of years ago women weren't talking about it nearly as openly as they are now. I was in my mid-thirties before women started telling me about the awful things they faced in the office, and it was a couple of years after that that I started encountering discussion of it online/in the media. I really hope we're now reaching a critical mass that's impossible to ignore.)